The invention relates to a godet for heating an advancing filament yarn.
U.S. Pat. No. 3,508,024 describes a godet for heating an advancing yarn wherein the godet has more than two axially adjacent stationary primary windings and a magnetically conductive godet jacket. The jacket is supported for rotation in concentric relationship with the primary windings, and is inductively connected with the primary windings via a narrow radial clearance for generating secondary currents. The carrier of the primary windings is built up from several laminated transformer sheets, which are arranged perpendicular to the axis of a coil support. A trigger circuit operates each of the primary windings with an alternating current of adjustable frequency, the primary windings being included in an oscillation circuit, which is adapted to the adjusted frequency. Via corresponding power switches in cooperation with associated temperature controllers, the oscillation circuit can be connected or disconnected as a function of the temperature measured on the godet jacket.
A similar godet is described in GB 989,349, wherein a primary winding is mounted on a circular carrier arranged in concentric relationship with a hollow cylindrical godet jacket. In the same manner as in U.S. Pat. No. 3,508,024, all flat transformer sheets of the carrier accommodating the primary windings are laminated on a coil support in axial direction. With respect to the inner surface of the godet jacket, the laminated iron sheets are arranged such as to form annular air gaps radially concentric with the axis of rotation of the godet.
In general with such heated godets, the problem arises that the loss of the magnetic flux toward the outside, in particular toward the coil support is relatively great, since all flat transformer sheets of the carrier of the primary windings are laminated on the coil support in the axial direction. Likewise, the magnetic flux in the thus-constructed carrier is not optimal, since axially adjacent transformer sheets form boundary layers. To overcome these boundary layers, a certain energy is required, which causes a loss of power. In particular, in a high-frequency application at, for example, 2 kHz and higher, the power loss increases significantly because of thicker boundary layers.
It is therefore the object of the invention to provide a heatable godet of the above-outlined kind, which permits an optimal magnetic flux in the godet by preventing a leakage field within the godet jacket, in particular in the region of the channel bottoms of the carrier, and by reducing the power loss caused by the boundary layers.